Methods have been developed which are capable of epoxidizing functionalized olefins such as allylic alcohols to form epoxides having a high degree of optical purity. For example, U.S. Pat. Nos. 4,471,130 and 4,764,628 teach the epoxidation of allylic alcohols using racemic or non-chiral organic hydroperoxides and soluble titanium complexes containing optically active alkoxide substituents as catalysts. More recently, the use of chiral hydroperoxides in combination with certain transition metal catalysts has been proposed (U.S. Pat. No. 5,166,371). Unfortunately, such methods are apparently not capable of providing epoxide products in high enantomeric excess where the initial unsaturated substrate is unfunctionalized (i.e., does not contain an active hydrogen functional group such as hydroxyl).
It thus would be highly desirable to develop alternative synthetic methods by which unfunctionalized substrates may be epoxidized in an asymmetric manner to yield optically active products having a satisfactorily high degree of optical purity.